Many original equipment manufacturers of products such as toys, typewriters, appliances, desks and other office equipment have established very demanding performance characteristics for the coatings used on their products. At the present time, these performance characteristics are capable of being met only with high temperature cure coatings, and both solvent-based and water-based compositions are currently available for this purpose. As these manufacturers broaden their choice of substrates from steel and aluminum into a variety of plastic materials, it becomes unacceptable to use high temperature cure coatings. This is because the plastics typically used, such as Noryl synthetic thermoplastic resins, Lexan polycarbonate resins, polystyrene, ABS and injection molding grade polyesters, are thermoplastic and tend to soften and deform at the temperatures of 300.degree. F. and higher that are required to cure the existing coating compositions. Moreover, most such coatings are solvent-based and, for environmental reasons, it is preferred to use aqueous-based compositions to avoid the pollution problems associated with solvent-based compositions.
Typical performance characteristics that must be possessed by a topcoat composition for many of these products include texturing capability, resistance to solvents such as 1,1,1-trichloroethane commonly used as an ink stain cleaner and adhesive remover, impact resistance, gloss level, hardness, dry adhesion and humidity resistance, as well as other known performance characteristics. The coating properties that would give satisfactory performance for solvent resistance (hardness) and impact resistance (flexibility) are generally the hardest to achieve simultaneously in a coating composition because they tend to be somewhat incompatible in nature. Additionally, satisfactory adhesion to a variety of metal and plastic substrates is a difficult problem to resolve when using aqueous compositions which are considered desirable to employ for environmental control reasons.
It is therefore an object of the invention to provide an aqueous topcoat composition having desired performance characteristics of the type described that is capable of being used in connection with application to a variety of substrates, both metal and plastic, particularly thermoplastic substrates.
It is a further object of the invention to provide a novel emulsion suitable for use in a topcoat composition of the type needed to give the high performance characteristics needed on a variety of substrates by original equipment manufacturers.
These and other objects of the invention will become apparent in the course of the following disclosure.